It is known that air-blast circuit breakers release into the atmosphere a large quantity of air each time the circuit breaker is opened. It is necessary to compensate these air losses so as to avoid a reduction in pressure which is detrimental to the proper operation of the circuit breaker. The compensation must take place very rapidly since the circuit breaker may be subjected to opening and closing cycles which succeed one another at a high rate, the interval of time between two opening operations possibly being of the order of about a few tenths of a second.
Other smaller losses of air occur when the circuit breaker closes. Also, said circuit breaker generally has a low continuous leakage flow of air while it is in operation.
Conversely, the gas pressure of an air blast circuit breaker may increase due to an operational incident or even because of a rise in the outside temperature. In some cases, said pressure may reach a dangerous level for the safety of the installation.
It is known to compensate the air losses by using a large compressed air tank, said tank being connected permanently to the internal volume of the circuit breaker. Said disposition has the disadvantage of being expensive and of requiring periodic checks on the tank.
An injector is also known which is capable of systematically injecting a quantity of air into the circuit breaker each time it has been opened; the injection command is triggered by the opening command. Such an injector makes it possible to avoid having to install a large extra tank but has the disadvantage of causing an excess of pressure in the circuit breaker if the opening command is not effective.